1. Field of Invention
The present invention relates to a brightness enhancement film, and more particularly, to a light-diffusion brightness enhancement film suitable for use in a liquid crystal display (LCD).
2. Description of the Prior Art
Generally speaking, the structure of a liquid crystal display (LCD) mainly comprises two parts, i.e., a panel and a backlight module, where the panel includes, for example, an indium-tin-oxide (ITO) conductive glass, liquid crystals, an alignment film, a color filter, a polarizer, and a driving integrated circuit, and the backlight module includes, for example, a lamp, a light guide, and various optical films. In order to make an LCD exhibit desired viewing angles and colors, many attempts have been done in this regard. For example, it is known that the luminance of an LCD panel may be enhanced by increasing the number of lamps. Nevertheless, the increase in the number of lamps would result in the storage of an excess of heat in the structure so as to adversely-affect the shelf life and quality of other parts in the LCD. Moreover, it is necessary to consume more electricity, and this is not suitable for those information goods relying on battery power to provide to the required electricity. Up to now, there have been various optical films which can be used in back light modules to enhance the luminance of LCD panels and increase the efficiency of the light source, without the need of changing the design of the parts or consuming excess energy. Thus, the use of an optical film became a more economic and convenient approach for increasing luminance.
A brightness enhancement film, which is also known as a prism film, has a fine prism structure formed on a polyester optical film having a thickness of only 50-200 μm by curing a special acrylic resin with a high energy UV light on the polyester optical film. The main function of the brightness enhancement film is to collect the disordered light emitted from a light guide to various directions by refraction and total internal reflection, and direct the light to an on-axis direction of about ±35 degrees, so as to enhance the luminance of the LCD.
There are many patents disclosing the utilization of a brightness enhancement film in a backlight module. For example, WO 96/23649, filed by 3M Company, discloses a method for preventing the vertex angles of a condensing prism structure from collapsing and sinking, which method comprises heating a completed prism film to a temperature above the glass transition temperature of the resin, so as to increase the hardness of the vertex angles of the condensing prism structure. However, the brightness enhancement film disclosed in WO 96/23649, as shown in FIG. 1, has a condensing structure on only one surface and the other surface is smooth, which cannot effectively diffuse and then condense evenly the light from a light source, and thus results in a poor uniformity of light.
A common solution to the above problem used in industry is to place a diffusion film under the brightness enhancement film. However, this solution faces the disadvantages that the manufacture cost is increased and the backlight module becomes more complex. FIG. 2 is a schematic view of a conventional backlight module for condensing light. As shown in FIG. 2, a diffusion film (2) is disposed between a light source (1) and a brightness enhancement film (3). In view of the above, the present invention provides a brightness enhancement film for overcoming the above disadvantages. For example, according to an embodiment of the present invention, as shown in FIG. 3, a resin mixed with plastic particles is coated on the back surface of a brightness enhancement film of WO 96/23649, and then, the resin is molded by curing. With the brightness enhancement film of the present invention, the light is uniformized by the resin mixed with plastic particles and then condensed by the prism structure, thereby achieving a better light uniformity.